Abstract: 【Objective】To elucidate the expression pattern of the SRY-related high mobility group box protein 8 gene(Sox8) in red crucian carp(Carassius auratus red var.) and the impact of nonylphenol(NP) exposure on Sox8 gene expression during embryonic development, providing a scientific basis for uncovering the molecular mechanisms of NPinduced embryonic developmental deformities in red crucian carp. 【Method】The full-length cDNA sequence of Sox8 gene from red crucian carp was cloned using RACE technique. Bioinformatics analysis were conducted using online tools such as ProtParam, ProtScale, InterPro, PredictProtein and DeepTMHMM. Real-time fluorescence quantitative PCR was employed to detect the expression of Sox8 gene in various adult tissues and at different embryonic developmental stages, as well as the effect of different NP concentrations exposure on Sox8 gene expression during the embryonic stage of red crucian carp. 【Result】The full-length cDNA sequence of Sox8 gene in red crucian carp was 2163 bp, with an open reading frame(ORF) of 1176 bp encoding 391 amino acid residues. The relative molecular weight of the SOX8 protein was 43798.30 Da, with a theoretical isoelectric point(pI) of 6.90, a lipophilicity index of 49.92, an instability index of 66.04, and a grand average of hydropathicity(GRAVY) of-1.026. The N-terminus contained a Sox_N dimerization domain and an HMG-box domain. Phylogenetic analysis based on the SOX8 amino acid sequences revealed a close relationship between C. auratus red var. and Carassius carassius(common crucian carp). The Sox8 gene was broadly expressed in various adult tissues of red crucian carp, with the highest relative expression in the brain, which was significantly higher than that in other tissues(P<0.05, the same below). During embryonic development, Sox8 gene expression decreased gradually from post-fertilization to the 14-somite stage, but significantly increased from the 21-somite stage, maintained at a high level until the hatching stage. Under most conditions, NP exposure significantly affected Sox8 gene expression during embryonic development of red crucian carp, particularly activating Sox8 gene expression to varying degrees after the 14-somite stage. 【Conclusion】Sox8 gene expression exhibits tissue specificity in adult red crucian carp and presents a trend of initial decrease followed by increase during embryonic development. NP exposure significantly affects Sox8 gene expression during embryonic development, with the increased expression of Sox8 gene after the 14-somite stage potentially contributing to NP-induced embryonic deformities in red crucian carp.